The magnesium-specific uptake and translocation transporters ZmMGT10 and MGR6 are upregulated not only by magnesium deficiency but also by high potassium concentrations in maize.

The antagonism between potassium (K+) and magnesium (Mg2+) is the primary cause of Mg2+ deficiency worldwide. Recent studies have demonstrated that the suppressive effect of K+ on Mg2+ uptake is significantly reduced as the K+/Mg2+ ratio increases, as both cations share non-specific cation channels. Concomitantly, the relative root/shoot translocation of Mg2+ increased. In contrast, there are indications that elevated tissue [K+] impedes the primary physiological functions of Mg2+. In this study on Zea mays L., the involvement of the only known specific Mg2+ uptake transporter ZmMGT10 and that of the translocation transporter MGR6 was examined. In a hydroponic setup, young maize plants were subjected to eight distinct K+/Mg2+ ratios. Relative RNA expression of the two transporters was examined. In a second experiment, the effect of elevated leaf [K+] on the physiological functions of Mg2+ was investigated, while uptake antagonism was avoided. The maize plants here were subjected to a sufficient Mg2+ supply and absolute deficiency under conditions of adequate and excess [K+]. The analysis included chlorophyll values, starch, and nutrient concentration. While ZmMGT10;1 was higher expressed due to K+-induced lower root [Mg+2], ZmMGT10;2 showed a higher expression at high K+ exposure, although this response was independent of root [Mg+2]. A similar response was also observed for MGR6. It was found that the physiological functions of Mg2+ were not affected by increased [K+] in the tissue. In conclusion, the higher uptake and the elevated expression of translocation transporters were identified as an adaptation strategy of maize plants to K+-induced Mg2+ deficiency.